An image forming apparatus that includes a light source, a brushless motor and a rotating polygon mirror is known. In the image forming apparatus configured as described above, a light beam emitted from the light source is reflected off the mirror surface of the rotating polygon mirror which is driven to rotate by the brushless motor, and is guided to the surface of a photosensitive member. In this way, a scanning line produced by the light beam is formed on the surface of the photosensitive member.
In the image forming apparatus configured as described above, phase switching control that switches, with appropriate timing corresponding to the position of the rotor of the brushless motor, the energization/non-energization state of each phase of a stator is performed. The detection of the position of the rotor is performed with, for example, a plurality of Hall elements. A technology is proposed in which the detection of the position of the rotor is performed based on the value of an inductive voltage produced in a coil while the rotor is being rotated. In this technology, since it is not necessary to provide a sensor such as a Hall element for detecting the position of the rotor, it is possible to simplify the configuration of the apparatus and reduce the size and cost of the apparatus.